FIGS. 5(a) to 5(c) are cross-sectional views showing a prior art method for asymmetrical ion implantation relative to a refractory metal or a refractory metal silicide electrode. In the figures a refractory metal or a refractory metal silicide electrode 1 is disposed on a compound semiconductor substrate 2. Reference numeral 5 denotes a photoresist covering substrate 2 at only one side of the electrode 1 and a portion of electrode 1. Reference numeral 4 denotes a region of the substrate 2 in which ions are implanted using the resist 5 and the electrode 1 as a mask.
A production method of the device will be described.
First of all, as shown in FIG. 5(a), a refractory metal or a refractory metal silicide is deposited on the entire surface of the compound semiconductor substrate 2 and etched to produce a desired configuration of electrode 1.
Next, as shown in FIG. 5(b), a photoresist 5 is deposited and paterned by photolithography so that one side of the electrode 1 is completely covered from the top surface of the electrode 1 to the substrate 2. Thereafter, ions are implanted using the photoresist 5 and the electrode 1 as a mask.
Subsequently, as shown in FIG. 5(c), after the photoresist 5 is removed, activate the implanted impurity ions are activated by annealing, thereby to produce an active region 4.
Thus, a semiconductor device having an active region at only one side of the refractory metal or refractory metal silicide electrode is completed.
In the prior art method, the photoresist 5 is used as a mask for ion implantation relative to the refractory metal or refractory metal silicide electrode 1. Therefore, it is necessary to pattern the photoresist 5 in alignment with the top surface of the electrode 1 which is difficult when the electrode is narrower than the mask alignment precision. For example, when the mask alignment precision is in a range of .+-.0.2 micron, the width of the electrode must be at least 0.4 micron to adjust the edge of the photoresist 5 to the center of the electrode 1. Actually, an electrode finer than 0.6 micron cannot be produced.